Rare earth elements (15 elements such as yttrium, scandium, and lanthanide) are used for a permanent magnet, a fluorescent material, a glass abrasive, high refractive index glass, and a hydrogen storing alloy or the like. The rare earth elements are indispensable elements.
Although many rare earth elements exist in comparatively abundant resource amounts, concentrated minerals are unevenly distributed on the earth, and are not produced in Japan. The rare earths are heavy metals, and are harmful if the rare earths are emitted into the environment. For this reason, the rare earth elements are desirably reused from products or wastes.
Although high-concentration rare earth ions can be precipitated and removed by pH control or the like, low-concentration rare earth ions can be removed with the use of an ion-exchange resin or a chelating resin.
However, in these techniques, all the rare earths and heavy metals are precipitated, or adsorbed by a resin, which makes it difficult to reuse the rare earths.
It is known that a compound having a phosphate group can selectively adsorb rare earth ions. For example, it has been known that aluminum can be separated from cerium with the use of a rare earth adsorbent using carbamyl methylphosphoric acid.
A polymer obtained by subjecting a phosphate group to graft polymerization has been known. Patent Literature 1 discloses that milt having a phosphate group can be used as a rare earth adsorbent, and iron can be separated from neodymium and dysprosium which are rare earths. However, there is a problem that phosphorus itself may be depletion resource.
On the other hand, a metal selective adsorbent used in an ion imprint method has been known. Particularly, an erbium (Er) selective adsorbent containing 5,7-dichloro quinolone-8-ol and 4-vinyl pyridine as ligands, or the like has been known.